1. Field of the Invention
This invention relates to an engine unit including an engine and a power train for transmitting the output power to the driving wheels.
2. Description of the Prior Art
In a vehicle, an engine is sometimes mounted sideways so that its crankshaft extends in the transverse direction of the vehicle body. In such a vehicle, a transmission is generally mounted on the rear or front side of the engine to extend in parallel to the crankshaft in order to reduce the overall length of the engine unit including the engine itself and the power train, and the engine output power is transmitted from the crankshaft to the transmission through suitable means such as a chain, gears and the like. (See U.S. Pat. No. 4,915,070, Japanese Unexamined Patent Publication Nos. 63(1988)-103735 and 1(1989)-316560 and the like.)
In order to compactly arranging the engine unit, it may be preferred that the engine body and the power train be supposed in an integral housing. However, such an attempt can encounter difficulties in machining and assembly of the parts depending on the arrangement of the bearings for the respective shafts.
That is, generally the housing of the engine body (in the cylinder block) is divided into upper and lower parts at a portion supporting the crankshaft and the bearings for supporting the crankshaft are formed in the mating surfaces of the upper and lower parts. However if the housing of the engine body is further divided at a portion supporting the transmission shaft and the bearings for supporting the transmission shaft are formed there, the number of the parts forming the engine housing increases, which is not preferable in view of machining and assembly of the parts. In order to incorporate the transmission shaft and the like without further dividing the engine housing, the transmission shaft must be inserted into the engine housing through an opening formed in the wall of the engine housing. The opening must be larger in diameter than the transmission shaft and the transmission shaft must be provided at its end with a journal portion which conforms to the opening in diameter, which adds to the weight of the shaft and gives rise to a problem in strength.
In Japanese Utility Model Publication No. 48(1973)-22886, there is disclosed a power train mechanism in which the casing for housing a transmission and a front differential is formed integrally with a crank case and the bearing portions for the crankshaft and the bearing portions for the transmission shaft or drive shafts for the front wheels are formed in the same mating surfaces at which the integrated casing is divided. This power train mechanism is disadvantageous in that the bearing portions must be large in thickness in order to ensure sufficient supporting rigidity.